A. Field of the Invention
This invention relates to the preparation of N-halogenated organic heterocyclic compounds which have particular application in treating water, such as disinfecting or controlling the biofouling of the water.
B. Description of the Prior Art
Halogens, especially chlorine and bromine, have long been used for water treatment since they exhibit a broad spectrum of bactericidal activity at low concentrations. Of the two, chlorine has a wider application, being supplied as a pure gas in pressurized cylinders, or alternatively, as a liquid or solid hypochlorite containing 5 to 70% by weight available chlorine. Dosage of these concentrated forms of chlorine is so small that finely calibrated metering devices are required for field use. Furthermore, chlorine residuals in water must be maintained within close tolerances, since concentrations only slightly higher than the effective minimum are often irritating to the eyes, nose and skin. To maintain chlorine residuals within close tolerances requires careful metering of the chlorine and precise performance of the sensitive gas injectors or liquid metering pumps. Since these mechanical devices are continuously exposed and subjected to a highly corrosive environment, malfunction of the devices is common. This can result in dangerously high concentrations of chlorine in the water or, conversely, chlorine residuals can become so low as to be bactericidally ineffective.
Another factor which makes the maintenance of satisfactory chlorine residuals difficult with conventional metering equipment is the varying chlorine demand of the water, particularly as exemplified by the continuously changing requirements for chlorine in a swimming pool. For instance, during heavy use, the chlorine residual requirements will increase greatly for water disinfection. To properly compensate for such variable chlorine requirements involves frequent manual resetting of the metering device. Attempts have been made to correct this shortcoming by providing sensors in the treated water with feedback controls to the chlorine feeder to continuously readjust the pumping rate. Such systems are expensive and can themselves malfunction.
Bromine is an excellent water disinfectant but has very limited use in the present art because liquid bromine causes severe burns if allowed to contact the skin, and its fuming vapors are highly corrosive and toxic. Inorganic hypobromites have not been successfully offered in commerce since they are extremely unstable, reverting in a short period of time to germicidally inactive bromate.
In an effort to overcome the foregoing problems, N-halogenated organic compounds such as N-brominated-N-chlorinated organic compounds have been developed for water treatment. An advantage of these compounds is that they are solids which makes them relatively safe to handle. In addition, they may contain high percentages of bromine, as well as chlorine, which affords the further advantage of being able to maintain good halogen residuals in water.
When N-halogenated organic heterocyclic compounds, such as N-bromo-N'-chloro-5,5-dimethylhydantoin are utilized for water treatment, it is necessary that they have sufficient particle size. The reason for this requirement is that the compounds must exhibit good solubility in water but have a relatively low solubility when they have sufficient particle size, such as in the form of a cohesive solid mass. Low solubility of the compounds having sufficient particle size allows them to be immersed in the water for long periods of time without substantial loss of potency.
In addition, it is desirable that N-halogenated organic heterocyclic compounds have sufficient particle size because of the very dusty and corrosive nature of the compounds. Airborne particles of the N-halogenated organic heterocyclic compounds can cause an unsatisfactory work environment and high maintenance costs in equipment coming into contact with the compounds.
When the N-halogenated heterocyclic organic compound particles have sufficient size, dissolution of the particles is restricted to the outer surface of the particle which allows them to be immersed in water for long periods of time without a substantial loss of potency. In addition, restricting the dissolution ratio of the particles allows a controlled addition of the halogens to the water. This allows the N-halogenated organic heterocyclic compounds to perform as a chemical sensor which is capable of an autonomic response. Because of this property, the dissolution rate of the particles in water increases in response to the contamination load in the water.
Methods of preparing N-halogenated organic heterocyclic compounds are known. For instance, U.S. Pat. No. 3,147,259 discloses the preparation in an aqueous alkaline medium of such compounds by treating an N-hydrogen organic heterocyclic compound, having at least two N-hydrogen radicals, with chlorine in the presence of a bromine-producing chemical. German Pat. No. 2,503,049 discloses the preparation of N-bromo-N-chloro-5,5-dimethylhydantoin by reacting 5,5-dimethylhydantoin in an aqueous alkali carbonate solution containing a wettiing agent at a temperature of 0.degree. to 15.degree. C. U.S. Pat. No. 3,345,371 discloses the preparation of N-brominated-N-chlorinated organic heterocyclic compounds by mixing a multi-N-brominated organic heterocyclic compound with a multi-N-chlorinated organic heterocyclic compound. U.S. Pat. No. 3,412,021 discloses the preparation of particles of N-halogenated organic heterocyclic compounds in the form of a cohesive mass by utilizing a binder and compressing the particles into a compacted mass, such as by tableting or briquetting.
A problem associated with compressing particles of N-halogenated organic heterocyclic compounds into a compacted mass to obtain proper size is the added expenses of the equipment necessary for compressing the particles and the additional necessity of first preparing the N-halogenated compounds prior to compressing them into a cohesive mass. Since the N-halogenated organic heterocyclic compounds are corrosive, this results in high maintenance cost of the equipment used therein and associated dusting problems.
The present invention provides a method of preparing N-halogenated organic heterocyclic compounds which overcomes or at least mitigates the above described problems.